Your first selection ...

Your first selection criteria would be to determine the quality requirements of the end products, principally in terms of hardness and sodium. NF is also called the softening membrane process because it preferentially removes CA and MG hardness (>90%) but removes NA and CL at 50%. RO removes all ionic constituents at >90-98%. That's why RO membranes are generally more expensive than NF membranes and you should select NF is it meets your quality requirements without an overkill. I think you get the picture.